The invention relates to a method for the production of hot-finished seamless pipes having optimized fatigue properties in the welded state. The invention also relates to a pipe produced with this method.
Different methods for producing seamless pipes are described, for example, in Stahlrohr Handbuch (Vulkan-Verlag, Essen, 12. Auflage 1995, S.97-101). (Handbook of Steel Pipes, published by Vulkan-Verlag, Essen, 12th edition 1995, page 97-101).
The pipes produced by this method find applications, for example, in the oil and gas extraction technology, wherein the individual pipe sections are butt-welded to form a continuous run.
A precise geometric match of the pipe ends to be welded with tight tolerances is required for forming the pipe connection so as to attain a high fatigue resistance of the weld connection during operation of the pipeline. To eliminate geometric notches, care needs to be exercised that the pipe ends to be welded together do not have offset edges.
The exact geometry and tight tolerances of the pipe ends to be welded together are important not only for meeting the strict requirements relating to fatigue resistance, but also for meeting the production costs of the weld connection.
The weld connection can be produced cost-effectively and efficiently, for example by automatic welding, only if the pipe ends to be welded together are exactly aligned with tight tolerances, which also ensures a high fatigue resistance of the weld connection. A substantially unimpeded flow of the medium through the pipeline is also guaranteed only under these circumstances.
Under realistic production conditions, the tolerances of hot-rolled seamless pipes cannot be maintained with the tight tolerances required for an efficient production of the connecting weld. In addition, small variations in the wall thickness and ovality in the pipe diameter can occur.
The ends of the pipes to be welded must be selected and matched to one another commensurate with their geometry. To date, such intentional matching has been possible only by taking actual measurements of the pipe ends.
WO 2005/031249 discloses an apparatus which measures the inside and outside geometry of pipe ends and thus makes it possible to intentionally select pipe ends with an exact match.
Disadvantageously, this process requires complicated logistics for storage and transport of the pipes to make sure that pipes with matching geometry are always on hand for a trouble-free manufacture. As another disadvantage, the production becomes inflexible during a malfunction, for example, if no pipe with matching geometry is available for a weld connection to a pipeline end.